ESS topic 4.4 Water pollution (new syllabus)

Water pollution (4.4.1)

Addition of harmful substances to water bodies that can have major impacts on marine and freshwater systems. The Flint River in Michigan, USA was historically used as an unofficial waste disposal site for refuse from local industries, car factories, meat packaging firms, and paper mills.

Plastic debris (4.4.2)

Accumulation of non-biodegradable plastic materials in marine environments that threatens ocean health and safety. The Great Pacific Garbage Patch, an area of marine debris in the North Pacific Gyre, contains an estimated 100 million tonnes of plastic waste and covers approximately 700,000 km² to 15,000,000 km² of ocean surface.

Microplastics (4.4.2)

Small plastic particles less than 5 mm in diameter that result from the breakdown of larger plastic items. These have been found in tap water, salt, and beer worldwide, and can contain chemicals used in plastic production that are carcinogenic when ingested by marine organisms.

Water quality (4.4.3)

Measurement of chemical, physical and biological characteristics of water that can determine its suitability for various uses. In freshwater aquatic systems, it is assessed by monitoring dissolved O₂, pH, temperature, turbidity, and concentrations of nitrates, phosphates, specific metals and total suspended solids.

Turbidity (4.4.3)

Measure of the amount of suspended sediment present in a water sample, which impacts light penetration. Following heavy rainfall, soil erosion from agricultural fields can give water a murky appearance, potentially harming aquatic life that depends on clear water.

Biochemical oxygen demand (BOD) (4.4.4)

Measure of the amount of dissolved oxygen required by microorganisms to decompose organic material in water. It is used to indirectly measure the amount of organic matter in a sample and is usually measured as milligrams of O₂ per liter of water (mg O₂ l⁻¹).

Eutrophication (4.4.5)

Process that occurs when lakes, estuaries and coastal waters receive inputs of mineral nutrients, especially nitrates and phosphates, often causing excessive growth of phytoplankton. During the 1960s, Lake Erie (on the USA-Canada border) experienced rapid changes that produced algal and cyanobacterial blooms, which caused changes in water quality and reduced biodiversity.

Hypoxia (4.4.6)

Condition of low oxygen in water bodies (typically less than 2 mg/L) caused by excessive growth of phytoplankton followed by their death and decomposition. In Lake Erie, the decomposition of increased lake phytomass killed invertebrates and fish as oxygen levels declined due to respiration of decomposer organisms.

Anoxia (4.4.6)

Complete absence of oxygen in water, occurring in severely eutrophic systems when oxygen demand from decomposition exceeds supply. In autumn, the growth of algae and cyanobacteria resulting from increased levels of nutrients in the water at higher temperatures can result in oxygen starvation in the water, leading to fish deaths.

Ecosystem services (4.4.7)

Benefits that healthy ecosystems provide to humans, which can be substantially impacted by eutrophication. Eutrophication can negatively affect fishing, recreation, aesthetics, and human health; for instance, growth of large macrophytes can reduce access to waterways for fishing, sailing, and other activities.

Non-biodegradable pollutants (4.4.9, HL)

Substances that persist in the environment because they cannot be broken down by natural processes, often becoming biomagnified in food chains. Pollutants like PCBs, DDT, and mercury are absorbed within microplastics and increase in concentration along food chains, reaching harmful levels in top predators.

Indicator species (4.4.13, HL)

Species that are sensitive to pollutants or adapted to polluted waters, providing information about environmental conditions. Certain macroinvertebrates like stonefly larvae serve as evidence of clean water, while organisms like rat-tailed maggots can survive in heavily polluted conditions.

Biotic index (4.4.14, HL)

An indirect measure of water quality based on the tolerance to pollution, relative abundance, and diversity of species in the community. The Trent index assesses water quality by examining the presence or absence of certain indicator species of macroinvertebrates that have varying tolerance to pollution.

Water quality index (WQI) (4.4.15, HL)

A single, weighted average combining the results of several individual water quality test parameters, representing the degree of contamination in a water sample. Chemical indicators for water quality indices include dissolved oxygen (where 75% oxygen saturation indicates healthy, clean water), pH (where 7 is neutral), phosphate and nitrate levels.